* {
  margin: 0;
  padding: 0;
}
html,
body,
.wrapper {
  width: 100%;
  height: 100%;
}

.btn {
  background-color: #ccc;
  color: #ff0000;
  width: 100px;
  height: 100px;
  margin: 100px auto;
  padding: 50px;
}

.header{
  position: fixed;
  top: 0;
  left: 0;
  background: #303643;
  width: 100%;
  height: 40px;
  color: #fff;
  text-align: center;
  line-height: 40px;
}
.header .icon1,
.header .icon2{
  width: 30px;
  position: absolute;
  top: 4px;
}
.header .icon1{
  left: 10px;
}
.header .icon2{
  right: 10px;
}
.header img{
  width: 100%;
}
.main{
  margin-top: 40px;
  min-height: 100%;
}